1. Field of the Invention
The present invention relates to a disk array device, more particularly, to a technology of controlling area allotment of a memory mounted on the disk array device.
2. Description of the Related Art
Currently, a data volume to be handed in business organizations and so on is increasing day by day in accordance with the development of information infrastructure. As a method of saving important information such as customer data and order data, disk array devices of SAN (Storage Area Network)/NAS (Network Attached Storage) type are rapidly coming into wide use. A disk array device includes a large-capacity storage device constituted of a plurality of hard disks (magnetic disk devices) and it reads/writes data from/to the hard disks in response to a request from a server and so on.
Such a disk array device is indispensable for configuring the information infrastructure such a society system. Therefore, there is a strong demand for realizing a disk array device having both high reliability and high availability whose setting are flexibly variable while continuing its nonstop operation.
Further, in order to realize high-speed data transfer to improve the performance of the whole system, a computer system including a disk array device generally has a memory called a cache memory (hereinafter, also simply referred to as a “cache”) which can be accessed at a higher speed than a main storage device (for example, a magnetic disk device in a case of the aforesaid disk array device). In such a computer system, data read from the main storage device is temporarily stored in the cache, and if requested data exists in the cache, the cache is accessed, thereby reducing the number of accesses to the main storage device to realize higher speed of processing.
Here, in the computer system including the cache, as the capacity of the cache is larger, the number of accesses to the main storage device can be generally reduced, resulting in a higher processing speed. However, a memory used as the cache is higher in bit cost than the main storage device, and is often used as a memory for storing control information (data) relating to other functions such as, for example, an OS (operating system). Accordingly, the capacity usable as the cache is limited. There have been proposed technologies for optimizing a cache function realized by the use of a cache according to the operational status or the like of a computer system (see, for example, Japanese Patent Application Laid-open No. 2000-227866, Japanese Patent Application Laid-open No. Hei 11-288387, Japanese Patent Application Laid-open No. Hei 7-72981, and so on).
Generally, in a computer system including a cache, a higher performance can be realized as the capacity of the cache is larger. This also applies to a disk array device. Conventionally, in a memory mounted on a disk array device, a system memory area used by an OS and a firmware for management (system area) and a memory area used as a cache (cache area) are set upon power-on, and the sizes of these areas are fixed and unchangeable while the device is in operation. Specifically, in setting memory areas upon power-on, the maximum capacity necessary for operational processing of the device is secured as the system area and the remaining capacity is allotted as the cache area.
However, in the conventional disk array device, the maximum capacity secured as the system area also includes, for example, an area that is used only temporarily for specific processing operation while the device is in operation but is not used constantly. Such an area is scarcely used in actual operation but cannot be used as the cache memory, so that the memory is not effectively used (resulting in lower use efficiency of the memory).